Symptoms of lesions of the radial nerve and its branches

The radial nerve is formed from the posterior cord of the brachial plexus and is a derivative of the ventral branches of the CV - CVIII spinal nerves. The nerve descends along the posterior wall of the axillary fossa, being located behind the axillary artery and sequentially located on the belly of the subscapularis muscle and on the tendons of the latissimus dorsi and teres major muscles. Having reached the brachiomuscular angle between the inner part of the shoulder and the lower edge of the posterior wall of the axillary fossa, the radial nerve adjoins a dense connective tissue band formed by the junction of the lower edge of the latissimus dorsi and the posterior tendinous part of the long head of the triceps brachii. Here is the site of possible, especially external, compression of the radial nerve. Further, the nerve lies directly on the humerus in the groove of the radial nerve, otherwise called the spiral groove. This groove is limited by the attachment sites of the external and internal heads of the triceps brachii to the bone. This forms the radial nerve canal, also called the spiral, brachioradialis or brachiomuscular canal. In it, the nerve describes a spiral around the humerus, passing from the inside and back in an anterolateral direction. The spiral canal is the second site of potential compression of the radial nerve. From it, branches approach the triceps brachii and ulnaris muscles on the shoulder. These muscles extend the upper limb at the elbow joint.

A test to determine their strength: the subject is asked to straighten the limb, which has been slightly bent at the elbow joint; the examiner resists this movement and palpates the contracted muscle.

The radial nerve at the level of the outer edge of the shoulder at the border of the middle and lower thirds of the shoulder changes the direction of its course, turns in front and pierces the outer intermuscular septum, passing into the anterior compartment of the shoulder. Here the nerve is especially vulnerable to compression. Below, the nerve passes through the initial part of the brachioradialis muscle: it innervates it and the long radial extensor of the wrist and descends between it and the brachialis muscle.

The brachioradialis muscle (innervated by segment CV - CVII) flexes the upper limb at the elbow joint and pronates the forearm from the supination position to the midline position.

A test to determine its severity: the subject is asked to bend the limb at the elbow joint and simultaneously pronate the forearm from the supination position to the middle position between supination and pronation; the examiner resists this movement and palpates the contracted muscle.

The extensor carpi radialis longus (innervated by segment CV - CVII) extends and abducts the wrist.

Test to determine muscle strength: the wrist is asked to be extended and abducted; the examiner resists this movement and palpates the contracted muscle. After passing the brachialis muscle, the radial nerve crosses the capsule of the elbow joint and approaches the supinator. In the elbow region, at the level of the lateral epicondyle of the humerus or a few centimeters above or below it, the main trunk of the radial nerve divides into a superficial and a deep branch. The superficial branch goes along the infrabrachioradialis muscle to the forearm. In its upper third, the nerve is located outside the radial artery and above the styloid process of the ray passes through the space between the bone and the tendon of the brachioradialis muscle to the dorsal surface of the lower end of the forearm. Here this branch divides into five dorsal digital nerves (nn. Digitales dorsales). The latter branches out in the radial half of the dorsal surface of the hand from the nail phalanx of the first, middle phalanx of the second and radial half of the third fingers.

The deep branch of the radial nerve enters the gap between the superficial and deep bundles of the supinator and is directed to the dorsal surface of the forearm. The dense fibrous upper edge of the superficial bundle of the supinator is called the arcade of Froese. The most likely place for the occurrence of radial nerve tunnel syndrome is also located under the arcade of Froese. Passing through the canal of the supinator, this nerve is adjacent to the neck and body of the radius and then exits onto the dorsal surface of the forearm, under the short and long superficial extensors of the wrist and fingers. Before exiting onto the dorsum of the forearm, this branch of the radial nerve supplies the following muscles.

1. The extensor carpi radialis brevis (innervated by the CV-CVII segment) is involved in the extension of the wrist.
2. The supinator (innervated by segment CV-CVIII) rotates and supinates the forearm.

A test to determine the strength of this muscle: the subject is asked to supinate the limb extended at the elbow joint from a pronated position; the examiner resists this movement.

On the dorsal surface of the forearm, the deep branch of the radial nerve innervates the following muscles.

The extensor digitorum carpi (innervated by segment CV - CVIII) extends the main phalanges of the II - V fingers and simultaneously the hand.

A test to determine its strength: the subject is asked to straighten the main phalanges of the II - V fingers, when the middle and nail ones are bent; the subject resists this movement.

The extensor carpi ulnaris (innervated by segment CVI - CVIII) extends and adducts the wrist.

A test to determine its strength: the subject is asked to extend and adduct the wrist; the examiner resists this movement and palpates the contracted muscle. The continuation of the deep branch of the radial nerve is the dorsal interosseous nerve of the forearm. It passes between the extensors of the thumb to the wrist joint and sends branches to the following muscles.

The long muscle that abducts the pollicis longus (innervated by segment CVI - CVIII) abducts the first finger.

A test to determine its strength: the subject is asked to move his finger away and slightly straighten it; the examiner resists this movement.

The short extensor of the pollicis (innervated by segment CVI-CVIII) extends the proximal phalanx of the first finger and abducts it.

A test to determine its strength: the subject is asked to straighten the proximal phalanx of the first finger; the examiner resists this movement and palpates the tense tendon of the muscle.

The long extensor of the pollicis (innervated by segment CVII-C VIII) extends the distal phalanx of the first finger.

A test to determine its strength: the subject is asked to straighten the nail phalanx of the first finger; the examiner resists this movement and palpates the tense tendon of the muscle.

The extensor of the index finger (innervated by segment CVII-CVIII) extends the index finger.

A test to determine its strength: the subject is asked to straighten the second finger; the examiner resists this movement.

The extensor of the little finger (innervated by segment CVI - CVII) extends the V finger.

A test to determine its strength: the subject is asked to straighten the fifth finger; the examiner resists this movement.

The posterior interosseous nerve of the forearm also gives off thin sensory branches to the interosseous septum, the periosteum of the radius and ulna, and the posterior surface of the wrist and carpometacarpal joints.

The radial nerve is predominantly motor and supplies mainly the muscles that extend the forearm, hand, and fingers.

To determine the level of damage to the radial nerve, it is necessary to know where and how the motor and sensory branches depart from it. The posterior cutaneous nerve of the arm branches off in the area of the axillary exit. It supplies the dorsal surface of the arm almost to the olecranon. The posterior cutaneous nerve of the forearm separates from the main trunk of the nerve in the brachial angle or in the spiral canal. Regardless of the place of branching, this branch always passes through the spiral canal, innervating the skin of the back of the forearm. Branches to the three heads of the triceps brachii muscle depart in the area of the axillary fossa, brachial angle and spiral canal. Branches to the brachioradialis muscle, as a rule, depart below the spiral canal and above the lateral epicondyle of the arm. Branches to the long radial extensor of the wrist usually depart from the main trunk of the nerve, although below the branches to the previous muscle, but above the supinator. Branches to the extensor carpi radialis brevis may arise from the radial nerve, its superficial or deep branches, but also usually above the entrance to the supinator canal. Nerves to the supinator may branch above or at the level of this muscle. In any case, at least some of them pass through the supinator canal.

Let us consider the levels of radial nerve damage. At the level of the brachial axillary angle, the radial nerve and the branches that branch off from it in the axillary fossa to the triceps brachii muscle can be pressed against the dense tendons of the latissimus dorsi and pectoralis major muscles in the tendinous angle of the axillary exit region. This angle is limited by the tendons of the two muscles mentioned and the long head of the triceps brachii muscle. Here, external compression of the nerve can occur, for example, due to improper use of a crutch - the so-called "crutch" paralysis. The nerve can also be compressed by the back of a chair in office workers or the edge of an operating table over which the shoulder hangs during surgery. Compression of this nerve is known to be caused by a cardiac pacemaker implanted under the skin of the chest. Internal compression of the nerve at this level occurs with fractures of the upper third of the shoulder. Symptoms of radial nerve damage at this level are distinguished primarily by the presence of hypoesthesia on the back of the shoulder, to a lesser extent by weakness of forearm extension, as well as the absence or decrease of the reflex from the triceps brachii. When stretching the upper limbs forward to the horizontal line, a "drooping or falling hand" is revealed - a consequence of paresis of hand extension in the wrist joint and II - V fingers in the metacarpophalangeal joints.

In addition, there is weakness of extension and abduction of the first finger. Supination of the extended upper limb is also impossible, whereas with preliminary flexion in the elbow joint, supination is possible due to the biceps muscle. Elbow flexion and pronation of the upper limb are impossible due to paralysis of the brachioradialis muscle. Hypotrophy of the muscles of the dorsal surface of the shoulder and forearm may be detected. The zone of hypesthesia covers, in addition to the posterior surface of the shoulder and forearm, the outer half of the dorsal surface of the hand and the first finger, as well as the main phalanges of the second and radial half of the third finger. Compression lesion of the radial nerve in the spiral canal is usually a consequence of a fracture of the humerus in the middle third. Nerve compression may occur soon after the fracture due to tissue edema and increased pressure in the canal. Later, the nerve suffers when it is compressed by cicatricial tissue or bone callus. In spiral canal syndrome, there is no hypesthesia in the shoulder. As a rule, the triceps brachii muscle is not affected either, since its branch is located more superficially - between the lateral and medial heads of this muscle - and is not directly adjacent to the bone. In this tunnel, the radial nerve is displaced along the long axis of the humerus during contraction of the triceps muscle. The bone callus formed after a humeral fracture can prevent such movements of the nerve during muscle contraction and thereby contribute to its friction and compression. This explains the occurrence of pain and paresthesia on the dorsal surface of the upper limb during extension at the elbow joint against the action of the resistance force for 1 minute with incomplete post-traumatic damage to the radial nerve. Painful sensations can also be caused by finger compression for 1 minute or tapping the nerve at the level of compression. Otherwise, symptoms similar to those noted with damage to the radial nerve in the area of the brachio-axillary angle are revealed.

At the level of the external intermuscular septum of the shoulder, the nerve is relatively fixed. This is the site of the most common and simplest compression lesion of the radial nerve. It is easily pressed against the outer edge of the radius during deep sleep on a hard surface (table, bench), especially if the head presses on the shoulder. Due to fatigue, and more often in a state of alcoholic intoxication, a person does not wake up in time, and the function of the radial nerve is switched off ("sleepy", paralysis, "garden bench paralysis"). With "sleepy paralysis" there are always motor losses, but at the same time there is never weakness of the triceps brachii, i.e. paresis of forearm extension and a decrease in the reflex from the triceps brachii. Some patients may experience loss of not only motor functions, but also sensory ones, but the zone of hypesthesia does not extend to the back of the shoulder.

In the lower third of the arm above the lateral epicondyle, the radial nerve is covered by the brachioradialis muscle. Here, the nerve can also be compressed by fractures of the lower third of the humerus or by displacement of the head of the radius.

Symptoms of radial nerve damage in the supracondylar region may be similar to "sleep paralysis". However, in the nervous case, there are no isolated losses of motor functions without sensory ones. The mechanisms of occurrence of these types of compression neuropathies are also different. The level of compression of the nerve approximately coincides with the place of the shoulder compression. In differential diagnostics, it is also helpful to determine the upper level of provocation of painful sensations on the back of the forearm and hand when tapping and finger compression along the projection of the nerve.

In some cases, compression of the radial nerve by the fibrous arc of the lateral head of m. triceps can be determined. The clinical picture corresponds to the above. Pain and numbness on the back of the hand in the area of the radial nerve supply can periodically increase with intensive manual work, during long-distance running, with sharp bending of the upper limbs at the elbow joint. In this case, compression of the nerve between the humerus and the triceps brachii occurs. Such patients are advised to pay attention to the angle of flexion in the elbow joint when running and to stop manual work.

A fairly common cause of damage to the deep branch of the radial nerve in the elbow joint and upper forearm is compression by a lipoma or fibroma. They can usually be palpated. Removal of the tumor usually results in recovery.

Other causes of damage to the branches of the radial nerve include bursitis and synovitis of the elbow joint, especially in patients with rheumatoid polyarthritis, fracture of the proximal head of the radial bone, traumatic aneurysm of the vessels, professional overexertion with repeated rotational movements of the forearm (conducting, etc.). Most often, the nerve is damaged in the canal of the supinator fascia. Less often, this occurs at the level of the elbow joint (from the place where the radial nerve passes between the brachialis and brachioradialis muscles to the head of the radius and the long radial flexor of the wrist), which is called radial tunnel syndrome. The cause of compression-ischemic damage to the nerve may be a fibrous band in front of the head of the radius, dense tendinous edges of the short radial extensor of the wrist or Froese's arcade.

The supinator syndrome develops with damage to the posterior interosseous nerve in the area of the Froese arcade. It is characterized by night pain in the outer parts of the elbow region, on the back of the forearm and, often, on the back of the wrist and hand. Daytime pain usually occurs during manual work. Rotational movements of the forearm (supination and pronation) especially contribute to the appearance of pain. Patients often note weakness in the hand, which appears during work. This may be accompanied by impaired coordination of hand and finger movements. Local pain is detected upon palpation at a point located 4-5 cm below the lateral epicondyle of the humerus in the groove radial to the long radial extensor of the wrist.

Tests are used that cause or increase pain in the arm, such as the supination test: both palms of the subject are firmly fixed on the table, the forearm is bent at an angle of 45° and placed in a position of maximum supination; the examiner tries to move the forearm into a pronation position. This test is performed for 1 minute, it is considered positive if pain appears on the extensor side of the forearm during this period.

Middle finger extension test: pain in the hand can be caused by prolonged (up to 1 min) extension of the third finger with resistance to extension.

There is weakness of the forearm supination, extension of the main phalanges of the fingers, sometimes there is no extension in the metacarpophalangeal joints. There is also paresis of the abduction of the first finger, but the extension of the terminal phalanx of this finger is preserved. With the loss of the function of the short extensor and the long abductor muscle of the thumb, radial abduction of the hand in the plane of the palm becomes impossible. With an extended wrist, there is a deviation of the hand to the radial side due to the loss of the function of the ulnar extensor of the wrist with the preservation of the long and short radial extensors of the wrist.

The posterior interosseous nerve can be compressed at the level of the middle or lower part of the supinator by dense connective tissue. Unlike the "classic" supinator syndrome caused by compression of the nerve in the area of the Froese arcade, in the latter case the symptom of finger compression is positive at the level of the lower edge of the muscle rather than the upper one. In addition, paresis of finger extension in the "lower supinator syndrome" is not combined with weakness of the forearm supination.

The superficial branches of the radial nerve at the level of the lower forearm and wrist can be compressed by a tight watch strap or handcuffs ("prisoner's palsy"). However, the most common cause of nerve damage is trauma to the wrist and lower third of the forearm.

Compression of the superficial branch of the radial nerve with a fracture of the lower end of the radius is known as "Turner's syndrome", and damage to the branches of the radial nerve in the area of the anatomical snuffbox is called radial tunnel syndrome of the wrist. Compression of this branch is a common complication of de Quervain's disease (ligamentitis of the first canal of the dorsal ligament of the wrist). The short extensor and long abductor muscles of the first finger pass through this canal.

When the superficial branch of the radial nerve is affected, patients often feel numbness on the back of the hand and fingers; sometimes a burning pain is noted on the back of the first finger. The pain can spread to the forearm and even to the shoulder. In the literature, this syndrome is called Wartenberg's paresthetic neuralgia. Sensory loss is often limited to a path of hypesthesia on the inner back of the first finger. Often, hypesthesia can extend beyond the first finger to the proximal phalanges of the second finger and even to the back of the proximal and middle phalanges of the third and fourth fingers.

Sometimes the superficial branch of the radial nerve thickens in the wrist area. Finger compression of such a "pseudoneuroma" causes pain. The tapping symptom is also positive when tapping along the radial nerve at the level of the anatomical snuffbox or styloid process of the radius.

Differential diagnosis of radial nerve damage is performed with spinal root syndrome CVII, in which, in addition to weakness of forearm and hand extension, there is paresis of shoulder adduction and hand flexion. If there are no motor deficits, the localization of pain should be taken into account. With CVII root damage, pain is felt not only on the hand, but also on the dorsal surface of the forearm, which is not typical for radial nerve damage. In addition, radicular pain is provoked by head movements, sneezing, and coughing.

Syndromes of the thoracic outlet level are characterized by the occurrence or increase of painful sensations in the arm when turning the head to the healthy side, as well as when performing some other specific tests. At the same time, the pulse on the radial artery may slow down. It should also be taken into account that if at the level of the thoracic outlet the part of the brachial plexus corresponding to the CVII root is predominantly compressed, then a picture similar to the lesion of this root described above arises.

Electroneuromyography helps to determine the level of radial nerve damage. It is possible to limit the study to the use of needle electrodes of the triceps brachii, brachioradialis, extensor digitorum and extensor index finger. In supinator syndrome, the first two muscles will be preserved, and in the last two, during their complete voluntary relaxation, spontaneous (denervation) activity can be detected in the form of fibrillation potentials and positive sharp waves, as well as at maximum voluntary muscle tension - the absence or slowing of motor unit potentials. When the radial nerve on the shoulder is stimulated, the amplitude of the muscle action potential from the extensor index finger is significantly lower than with electrical stimulation of the nerve below the supinator canal on the forearm. A study of latent periods - the time of nerve impulse conduction and the speed of excitation propagation along the nerve - can also help to establish the level of radial nerve damage. To determine the speed of excitation propagation, electrical stimulation is performed along the motor fibers of the radial nerve at various points. The highest level of irritation is the Botkin-Erb point, located a few centimeters above the clavicle in the posterior triangle of the neck, between the posterior edge of the sternocleidomastoid muscle and the clavicle. Below, the radial nerve is irritated at the exit from the axillary fossa in the groove between the coracobrachialis muscle and the posterior edge of the triceps brachii muscle, in the spiral groove at the level of the middle of the shoulder, as well as at the border between the lower and middle third of the shoulder, where the nerve passes through the intermuscular septum, even more distally - 5 - 6 cm above the lateral epicondyle of the humerus, at the level of the elbow (brachioradialis) joint, on the back of the forearm 8 - 10 cm above the wrist or 8 cm above the styloid process of the radius. Recording electrodes (usually concentric needle electrodes) are inserted into the site of maximum response to stimulation of the nerve of the triceps brachii, brachialis, brachioradialis, extensor digitorum, extensor index finger, long extensor pollicis longus, long abductor muscle or short extensor pollicis. Despite some differences in the points of nerve stimulation and the places of recording the muscle response, close values of the excitation propagation velocity along the nerve are obtained under normal conditions. Its lower limit for the "neck-axillary fossa" section is 66.5 m/s. On the long section from the supraclavicular Botkin-Erb point to the lower third of the shoulder, the average velocity is 68-76 m/s. In the area "axillary fossa - 6 cm above the lateral epicondyle of the humerus" the speed of excitation propagation is on average 69 m/s, and in the area "6 cm above the lateral epicondyle of the humerus - forearm 8 cm above the styloid process of the radius" - 62 m/s when abducting muscle potential from the extensor of the index finger. From this it is evident that the speed of excitation propagation along the motor fibers of the radial nerve on the shoulder is approximately 10% higher,than on the forearm. Average values on the forearm are 58.4 m/s (fluctuations are from 45.4 to 82.5 m/s). Since lesions of the radial nerve are usually unilateral, taking into account individual differences in the speed of excitation propagation along the nerve, it is recommended to compare the indicators on the diseased and healthy sides. By examining the speed and time of conduction of the nerve impulse starting from the neck and ending with various muscles innervated by the radial nerve, it is possible to differentiate pathology of the plexus and various levels of nerve damage. Lesions of the deep and superficial branches of the radial nerve are easily distinguished. In the first case, only pain in the upper limb occurs and motor loss may be detected, and superficial sensitivity is not impaired.

In the second case, not only pain is felt, but also paresthesia, there are no motor deficits, but superficial sensitivity is impaired.

It is necessary to differentiate compression of the superficial branch in the elbow area from its involvement at the level of the wrist or lower third of the forearm. The zone of painful sensations and sensory loss may be the same. However, the test of voluntary forced extension of the wrist will be positive if the superficial branch is compressed only at the proximal level when passing through the short radial extensor of the carpi radialis. Tests with percussion or digital compression along the projection of the superficial branch should also be carried out. The upper level, at which these effects cause paresthesia on the back of the hand and fingers, is a probable site of compression of this branch. Finally, the level of nerve damage can be determined by introducing 2-5 ml of 1% novocaine solution or 25 mg of hydrocortisone into this place, which leads to a temporary cessation of pain and/or paresthesia. If the nerve block is performed below the site of its compression, the intensity of painful sensations will not change. Naturally, it is possible to temporarily relieve pain by blocking the nerve not only at the level of compression, but also above it. To distinguish between distal and proximal damage to the superficial branch, 5 ml of 1% novocaine solution is first injected at the border of the middle and lower third of the forearm at its outer edge. If the block is effective, this indicates a lower level of neuropathy. If there is no effect, a repeated block is performed, but this time in the elbow joint area, which relieves pain and indicates an upper level of damage to the superficial branch of the radial nerve.

The study of excitation propagation along the sensory fibers of the radial nerve can also help diagnose the compression site of the superficial branch. Conduction of the nerve impulse along them is completely or partially blocked at the level of compression of the superficial branch. With partial blockade, the time and speed of excitation propagation along the sensory nerve fibers slow down. Various research methods are used. With the orthodromic method, excitation along the sensory fibers spreads in the direction of conduction of the sensory impulse. For this, the stimulating electrodes are placed on the limb more distally than the abducens. With the antidromic method, excitation propagation along the fibers in the opposite direction is recorded - from the center to the periphery. In this case, the electrodes located proximally on the limb are used as stimulating, and the distal electrodes - as abducens. The disadvantage of the orthodromic method, compared to the antidromic one, is that the former records lower potentials (up to 3 - 5 μV), which can be within the noise limits of the electromyograph. Therefore, the antidromic method is considered more preferable.

The most distal electrode (the stimulating one in the orthodromic method and the abducting one in the antidromic method) is best placed not on the dorsal surface of the 1st finger, but in the area of the anatomical snuffbox, approximately 3 cm below the styloid process, where a branch of the superficial branch of the radial nerve passes over the tendon of the long extensor of the thumb. In this case, the response amplitude is not only higher, but also subject to smaller individual fluctuations. The same advantages are achieved by placing the distal electrode not on the 1st finger, but on the space between the 1st and 2nd metatarsal bones. The average excitation propagation velocities along the sensory fibers of the radial nerve in the area from the leaf electrodes to the lower parts of the forearm in the orthodromic and antidromic directions are 55-66 m/s. Despite individual fluctuations, the excitation propagation velocity along symmetrical areas of the nerves of the extremities in individuals on both sides is approximately the same. Therefore, it is easy to detect a slowdown in the speed of excitation propagation along the fibers of the superficial branch of the radial nerve in case of its unilateral lesion. The speed of excitation propagation along the sensory fibers of the radial nerve is slightly different in individual areas: from the spiral groove to the elbow region - 77 m/s, from the elbow region to the middle of the forearm - 61.5 m/s, from the middle of the forearm to the wrist - 65 m/s, from the spiral groove to the middle of the forearm - 65.7 m/s, from the elbow to the wrist - 62.1 m/s, from the spiral groove to the wrist - 65.9 m/s. A significant slowdown in the speed of excitation propagation along the sensory fibers of the radial nerve in its two upper sections will indicate a proximal level of neuropathy. The distal level of damage to the superficial branch can be detected in a similar way.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ], [ 7 ]